Agreed, there are fictitious concepts, imaginary concepts, ones that don't correspond to reality.
Your statement could also be interpreted another way, as a universal that could be instantiated but has not been until now which is different than what I am talking about.
I am bringing up an eternally uninstantiable universal/concept, basically, one that cannot be instantiated.
(I am talking about something that I think does not exist i.e. there is no such thing).
A contradiction can't be instantiated. Yet the concept exists.
You will say that contradiction (similar to "nothing") is not a universal and yet I would argue that we identify contradictions all the time. A contradiction exists only in fact as a concept/universal, there is no metaphysical version of it. But if contradictions are metaphysical, then they have to exist.
I am going along because you argue universals/concepts do exist metaphysically, independent of consciousness.
In that paradigm, since uninstantiated universals exist independently of consciousness, they exist even if consciousness has never observed their instance.
So numbers could have existed without "things" to be counted. Such a universe does not exist and for me is unimaginable.
I am also arguing that the abstraction (number) would not exist if the act of counting has never been done (ever).
(I will respond to the rest of the post)